The terms you will meet in a roofing survey or quote in North Wales, explained without jargon. If anything here is unclear, call us on 01492 339 101 and we will talk it through.
Eight terms that come up repeatedly on North Wales roofing surveys, explained in plain English with local context. Call 01492 339 101 if you want any of them explained against your own roof.
Nail sickness is the corrosion of the iron or copper nails holding slates to the roof battens. As the nails weaken, slates begin to slip — first on steep and exposed slopes, then across the whole roof. Victorian Llandudno properties with original iron fixings are now 120–140 years old, and nail sickness is the single most common reason a sound Welsh slate roof needs re-slating.
Penrhyn Blue is the blue-grey roofing slate quarried at Penrhyn Quarry in Bethesda, North Wales. It roofed almost all of Llandudno's Victorian and Edwardian housing stock. Its distinctive colour, consistent cleavage and durability make it the correct repair and re-roof material for period North Wales properties, and it is generally expected within the Llandudno Conservation Area.
NHL (natural hydraulic lime) mortar is the correct bedding and pointing mortar for period masonry. It is softer and more breathable than Portland cement, so it flexes with thermal movement instead of forcing the brick face to spall. NHL 2 suits soft handmade brick; NHL 3.5 suits harder brick and exposed coastal chimney stacks in Llandudno.
Lead code is the thickness grading of rolled sheet lead under BS EN 12588, running from Code 3 (1.32mm) to Code 8 (3.55mm). Code 4 covers standard step and apron flashings; Code 5 is used for back gutters and, on Llandudno's salt-exposed coastal properties, wherever Code 4 would otherwise suffice; Code 6 is used for lead valleys.
Patination oil is applied to newly installed lead to promote a stable protective carbonate patina. Without it, salt-laden coastal air can produce a soft, soluble oxide that keeps eroding rather than protecting the surface, and rainwater run-off stains the masonry below. It is applied as standard on all new leadwork within Llandudno's coastal zone.
Mechanical ridge fixing — dry ridge systems such as Redland Dry-Fix or Marley Universal — secures each ridge tile to the batten with a stainless steel clip, independently of any mortar bed. On exposed North Wales coastal roofs where salt air erodes mortar in 8–15 years, mechanical fixings stop the recurring ridge tile displacement that mortar-only bedding causes.
GRP (glass reinforced plastic) fibreglass roofing is a seamless flat roof laminate applied wet on site and cured in place. Because it has no joints, it has no seam failure risk, and it typically lasts 25–35 years. It requires substrate and air temperatures above 5°C during installation, which restricts outdoor fitting windows in North Wales winters.
Roof fall is the designed slope of a flat roof toward its outlets, specified at a minimum of 1:80 — roughly 12mm per metre — under BS 6229. Inadequate fall leaves standing water that accelerates membrane degradation, adds structural load, and creates freeze-thaw stress at edge details through North Wales winters. Settled decks are a common cause of lost fall.
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